The invention is based on a control mechanism for a fuel metering system of a combustion engine of the general type described hereinafter. Amongst others, a fuel injection system is known in which the control mechanism creates injection impulses based on rpm or load signals. In this known system a switch is coupled with the throttle plate mechanism signaling the idling or overrunning of the combustion engine. While this fuel injection system does not pose any problems during normal operation, a correct operation during start-up and immediately thereafter cannot always be achieved. This is because at the beginning of the ignition process a fixed injection inpulse time is programmed in, but a change is made, after even a minor deflection of the air metering plate, to the normal injection time based on load and rpm signals. Considering the initially very small rpm values during the first deflection of the air metering plate a comparatively very high value of load is simulated and therefore a very large amount of fuel is supplied. In such as case instead of the combustion engine starting up and running smoothly, it will gradually die and have to be restarted.